This study focuses on the effects of p H and fluoride at different molar ratios of fluoride to Al(R F:Al) on the removal of cadmium(Cd~(2+)) and phosphate by Al coagulation. Fluoride at R F:Al≥ 3:1 inhibits the removal of Cd over wide Al dose ranges from 5 to 10 mg/L as Al. The removal of phosphate decreases significantly at high R F:Al of 10:1 whereas at lowered R F:Al(i.e., ≤ 6:1), an adverse effect is observed only at insufficient Al doses below 2 mg/L. Fluoride shows inhibitive effects towards the removal of Cd at p H 7 and 8 and that of phosphate at p H 6. Fluoride decreases the ζ-potential in both systems, and the decreasing extent is positively correlated to the elevated R F:Al. The Al fluoride interactions include the formation of Al–F complexes and the adsorption of fluoride onto Al(OH)_3 precipitates, i.e., the formation of Al(OH)n F m. Al–F complex formation inhibits Al hydrolysis and increases residual Al levels, and a more significant increase was observed at lower p H. Al–F complexes at high R F:Al complicate the coagulation behavior of Al towards both negative and positive ionic species. Moreover, fluoride at low R F:Al shows little effect on Al coagulation behavior towards Cd~(2+)and phosphate, and the spent defluoridation adsorbent,i.e., aluminum(Al) hydro(oxide) with adsorbed fluoride at R F:Al of below 0.1:1, may be reclaimed as a coagulant after being dissolved. This study focuses on the effects of p H and fluoride at different molar ratios of fluoride to Al (RF: Al) on the removal of cadmium (Cd 2+) and phosphate by Al coagulation. Fluoride at RF: Al ≧ 3 : 1 inhibits the removal of Cd over wide Al dose ranges from 5 to 10 mg / L as Al. The removal of phosphate decreases significantly at high RF: Al of 10: 1 while at lowered RF: Al (ie, ≤ 6: 1 ), an adverse effect is observed only at insufficient Al doses below 2 mg / L. Fluoride shows inhibitive effects towards the removal of Cd at p H 7 and 8 and that of phosphate at p H 6. Fluoride decreases the ζ-potential in both systems, and the decreasing extent is positively correlated to the elevated RF: Al. The Al fluoride interactions include the formation of Al-F complexes and the adsorption of fluoride onto Al (OH) _3 precipitates, ie, the formation of Al (OH) n F m. Al-F complex formation inhibits Al hydrolysis and increases residual Al levels, and a more significant increase was observed at lowe rp H. Al-F complexes at high RF: Al complicate the coagulation behavior of Al towards both negative and positive ionic species. Furthermore, fluoride at low RF: Al shows little effect on Al coagulation behavior towards Cd ~ (2+) and phosphate , and the spent defluoridation adsorbent, ie, aluminum (Al) hydro (oxide) with adsorbed fluoride at RF: Al of below 0.1: 1, may be reclaimed as a coagulant after being dissolved.